The present invention relates to a homokinetic universal joint used mainly for front wheel drive vehicles, and particularly to a tripod type homokinetic universal joint.
FIG. 21 is a prior art homokinetic universal joint which has an outer member 1 formed in its inner surface with three axially extending cylindrical track grooves 2, a tripod member 3 inserted into the outer member 1 and formed with three radially extending trunnions 4, which are received in the respective cylindrical track grooves 2, and a spherical roller 5 rotatably and axially slidably mounted on each trunnion 4 so as to engage on roller guide surfaces 6 formed at each side of the track groove 2.
In such a known tripod type universal joint, when a turning effort is transmitted with some working angle formed between the outer member 1 and the tripod member 3, each spherical roller 5 is oblique with respect to the roller guide surface 6 in the track groove 2, as shown in FIGS. 21 and 22, so that the roller 5 cannot do a normal rolling motion. In more detail, the spherical roller 5 tends to roll in the direction of the arrow in FIG. 21, but, since the track groove 2 is cylindrical and parallel to the axis of the outer member 1, the movement of roller 5 is governed by the track groove 2. This causes a slippage between the roller roller 5, and the slippage causes the temperature to rise, an axial thrust roller 5, and the slip causes temperature rise, axial thrust and vibration.
The inventors of the present invention ascertained that the abovesaid problem results from the combination of a spherical roller with a cylindrical groove. They investigated various arrangements to solve this problem, and proposed using a cylindrical roller rolling on flat roller guide surfaces, considering that a cylindrical roller can roll on a flat guide surface without suffering restriction. However, the arrangement having a cylindrical roller merely mounted on each trunnion of the tripod member will not function as a universal joint due to the fact that interference happens between the outer periphery of the cylindrical roller and the roller guide surfaces on the track groove when some working angle is formed between the shaft of the outer member and that of the tripod member.
As shown in FIG. 20, when some working angle is formed between the tripod member 3 and the outer member in a plane including roller 5C on one (4C) of the trunnions 4 and the axis O of the outer member, the axis of the tripod member 3 shifts from the axis O of the outer member to a point O'. The axis O' of the tripod member 3 tends to turn around the axis O of the outer member with a radius r. In this state, the other two trunnions 4a, 4b form an angle .gamma. in comparison with the state when no working angle is formed. Thus, the rollers 5a and 5b mounted on these trunnions 4a and 4b will take a position as shown in FIG. 20 by the dotted lines and will get stuck between the roller guide surfaces 6, so that this arrangement can not function as a universal joint.